Many metals and their compounds are soluble in acidic and basic solutions. Accordingly, many metal recovery processes use an acidic or basic solution, typically called a leach solution, for generating a mineral bearing solution which will subsequently yield the desired metal.
In these processes, the mineral bearing leach solution typically requires further concentration and purification before a final product can be obtained. A major technique used for this purpose is resin ion exchange. As an example, resin ion exchange is used in uranium recovery. In uranium recovery, use of resin ion exchange is based on the existence of anionic uranium complexes in the leach solution. Under correct conditions, the anionic uranium complexes can be selectively removed by a preferentially absorbing synthetic resin. Following resin absorption, a suitable eluting reagent can be used to strip the uranium complexes from the resin, thereby yielding a purified and concentrated solution. Subsequently, precipitation techniques are available to produce a final product.
Resin ion exchange apparatus typically includes one or more preferentially absorbing resin beds and means for alternately combining the resin with a series of solutions, e.g., a mineral bearing leach solution, a wash solution or drainage and an eluting solution. In the exchange apparatus, the resin extracts the mineral from the mineral bearing solution in a fluidized bed established when the solution and resin are combined. Subsequently, the eluting solution strips the mineral from the resin in a fluidized bed established when the eluting solution and resin are combined. Depending upon the mineral concentration in the eluting solution, the eluting solution may either be further concentrated and purified or processed for the removal of the final product.
To maintain exchanger efficiency, equipment operators find it desirable to monitor various characteristics of the resin ion exchange column. For example, operators find it desirable to monitor such characteristics as fluidized bed height; accumulation of foreign matter in the bed; solution clarity; resin color; and resin breakage.
By monitoring bed height, the operator is able to check solution velocity and avoid resin bed depletion. Specifically, solution flow through the fluidized bed causes the bed to expand, the greater the solution velocity through the bed, the higher the fluidized bed height. If left unchecked, excess solution velocity could cause the bed to rise sufficiently to push resin out of the chamber.
Foreign matter in the fluidized bed can clog the apparatus and disrupt solution flow. Therefore, it is important that foreign matter be detected and removed. This is especially true for recovery process which leach scrap materials such as tin cans, as these processes are likely to produce foreign matter of every type which can clog the apparatus.
Observation of resin color advises the operator of the extent to which the resin has realized its maximum absorption. Accordingly, resin color gives the operator some notice of the quality and quantity of resin absorption.
Finally by being aware of resin breakage, the operator is able to determine whether the process is proceeding properly. In normal operation, resin breakage typically does not occur. Accordingly, appearance of significant amounts of broken resin suggests some problem in the process. Further, the monitoring of resin breakage advises the operator of the extent to which the resin bed is being depleted.
In the past, it has not been possible to directly observe a commercially sized fluidized bed. While in small scale laboratory apparatus, one can construct the exchanger vessel from transparent material, permitting direct operator observation of fluidized bed parameters, this is not possible in commercially sized apparatus. Unlike smaller laboratory apparatus, full size commercial columns contain large amounts of resin and solution creating substantial forces on the vessel walls. Commercially sized vessels, therefore, must be made of materials sufficiently strong to withstand these forces. Transparent materials such as glass and plexiglas, while of sufficient strength for laboratory apparatus are of insufficient strength to handle the loading in full size commercial columns. Rather, high strength materials such as stainless steel must be used for commercial sized vessel walls. Accordingly, the operator is denied visual observation of the fluidized bed.
While equipment has been developed which attempts to automatically monitor certain parameters of a commercially sized fluidized bed, such apparatus has proven to be insensitive to various column characteristics. For example, photoelectric cells have been used in commercially sized apparatus to detect the fluidized resin bed-solution interface. Unfortunately however, such sensors are unable to detect the difference between resin and foreign matter and therefore are unable to detect foreign matter in the bed. This failure is of particular importance in mineral recovery from scrap materials where significant amounts of foreign matter are likely. Additionally, such automatic monitoring apparatus tends to be expensive and complicated to use.
Accordingly, it is an object of my invention to provide apparatus and method for visually monitoring an ion exchange fluidized bed.
It is a further objective of my invention to provide apparatus and method which permits the visual monitoring of various fluidized bed characteristics such as fluidized bed height, presence of foreign matter, resin color, resin breakage, and solution clarity.
It is yet a further objective of my invention to provide apparatus and method for visually monitoring a fluidized bed which is inexpensive to make and simple to use.